1. Field of the Invention
This invention relates in general to coating devices and particularly to an apparatus for coating substrates by vaporization under the simultaneous action of an ionized gas.
2. Description of the Prior Art
A method for the production of thin coats is known which includes the vaporization of a substance in a vacuum vaporization plant in the presence of an atmosphere which reacts chemically with the substance. In such a method a coating is deposited on the objects to be coated which corresponds to the chemical compound resulting from the chemical reaction. This method is used mainly for the production of oxide films in the deposit of oxidizable substances in an oxygen atmosphere of low pressure. Coatings of other compounds, for example, nitrides, sulfides etc., can also be produced in the same manner. It is noteworthy that many coats which are obtained in this way are practically light absorption free. Considerable light absorption which is very undesirable for many applications must be accepted if such compounds are to be deposited by vaporization even though these compounds are themselves absorption-free. Experience has shown that this leads frequently to a partial decomposition of the evaporated compounds so that the deposits of other chemical compositions, for example in the vaporization of oxides and suboxides are formed.
It has already been suggested in the art to effect the reactive vaporization in an atmosphere which contains ions of the compound-forming gas. It is known to provide for this purpose a gas discharge vessel in the vaporization chamber having a wall with an opening through which the ionized gas can escape into the vaporization chamber.
In the last few years there has been an increasing demand for the production of coats which have a minimum absorption so that they may be exposed, for example, to light currents of maximum intensity such as are produced by lasers without being destroyed. These and other application possibilities had the result that more attention has been paid recently to the method of reactive vaporization in an ionized atmosphere. Even if maximum freedom of absorption is not of importance, the reactive vaporization in an ionized atmosphere is of interest for the industrial production of thin coats, because tests have shown that it is possible in this way to produce a hard and adhesive coat at a higher vaporization rate and with better vacuum than it was heretofore possible.